An Experimental Study of Opposed Flame Spread along Various Thin Fuel Configurations in Microgravity

In the present study, opposed flow flame spread over several fuel configurations of thin cellulosic fuels are investigated experimentally in normal gravity and microgravity environments. The fuel is configured in different shapes, namely, planar, hollow cylindrical (circular duct), C channel, and L channel, with the help of specifically designed fuel sample holders. The flame spread phenomena are examined for each configuration in both normal gravity and microgravity environments under ambient conditions of 21% oxygen and 1 atm. pressure. The microgravity experiments are conducted using a 2.5 s drop tower facility. The flame spread rates are measured at various opposed flow speeds. The effective flow speed accounts for the induced reference buoyant flow speed and externally imposed flow. The flame spread rates for each configuration are plotted against the effective flow speed ranging from 10 cm/s to 40 cm/s. While there is a nonmonotonic increasing-decreasing flame spread rate trend with respect to the effective opposed flow speed for all configurations, the flame spread rate can vary significantly with changes in the configuration. The C-channel configuration shows the highest flame spread rate compared with the other configurations of the same scale and identical experimental conditions. The effect of fuel size on the flame spread rate is also investigated for the duct configuration. The flame spread rate is noted to increase with the increase in fuel diameter.